Extraction of zinc



Sept. 6, 1966 L. J. DERHAM 3,271,134

EXTRACTION OF ZINC Filed Aug. 5, 1963 2 Sheets-Sheet l p 6, 1966 1.. J.DERHAM EXTRACTION OF ZINC 2 SheetS -Sheet Filed Aug.

United States Patent 3,271,134 EXTRACTION 0F ZINC Leslie Jack Derham,Avonrnouth, England, assignor to The National Smelting Company Limited,London, England, a British company Filed Aug. 5, 1963, Ser. No. 299,888Claims priority, application Great Britain, Aug. 20, 1962, 31,919/ 62 14Claims. (Cl. 7587) The invention relates to a process for producing zincmetal by the reduction of finely divided oxidic zinciferous material.

In the pyrometallurgical production of zinc metal, zinc oxide isreduced, directly or indirectly,'by carbon. In both electrothermal andretort processes, the carbon appears mainly as carbon monoxide, so thatthe overall reaction is:

This reaction absorbs a large amount of heat, which in theelectrothermic process is provided by electrical energy and in theretort process is provided by heat generated in an external combustionchamber. Electrical energy is usually expensive, and the transmission oflarge amounts of heat through retort walls is also expensive andrestricts the amount of zinc that can be produced in a single smeltingunit.

In the blast furnace smelting of zinc, the heat required for thereduction of zinc oxide is generated in the furnace Where the zinc oxideis being reduced. This enables a large production of zinc to be attainedin a single unit and with a good full economy. However, one drawback ofthe zinc blast furnace is that it requires an expensive sinteringprocess to be carried out upon the charge to be fed to the furnace.

The present invention, like the blast furnace, has the advantage thatthe carbonaceous material introduced into the furnace acts as both afuel and a reducing agent, but the present invention has the furtheradvantage that it enables zinc to be reduced from zinc concentrate thathas been either flash-roasted or oxidized in a fluidized bed, and that afurther sintering of the charge is unnecessary. It can also treatpulverulent by-products such as flue dusts or granulated lead blastfurnace slag-s.

The invention consists in a method for extracting zinc from a finelydivided oxidic zinciferous material substantially free from volatizablearsenic and sulphur comprising the steps of: introducing the finelydivided oxidic zinciferous material and finely divided carbonaceousmaterial into, a generally circular and vertical reduction zone, andentraining the material by, a swirling spiral stream of anoxygen-containing gas at such temperature that reduction to zinc vapourtakes place and all other non-volatile components assume a moltenfree-flowing form; separating these other components; and condensing thezinc vapour to give metallic zinc.

The invention further consists in a method of extracting zinc comprisingthe steps of: introducing a mixture of (A) pulverulent oxidiczinciferous material substantially free from volatizable arsenic andsulphur and (B) a pulverulent carbonaceous reducing agent, into achamber; simultaneously introducing an oxygen-containing gas in such afashion as to impart a whirling, swirling, downwardly spiraling, motionto the gas within the chamber and to entrain the finely divided mixture;maintaining a temperature such that the zinc oxide is reduced to zincvapour while the carbon is oxidized to CO/CO mixture and any ganguematerial melts to a slag, separating the slag from the gas stream; andfeeding the zinc vapour to a condenser.

The invention still further consists in a method for extract-ing zincfrom a zinc-sulphide concentrate which con- 3,271,134 Patented Sept. 6,1966 "ice tains arsenic as an impurity, in which the zinc-sulphideconcentrate is roasted to remove nearly all the sulphur and produce acalcine consisting mainly of zinc oxide, this calcine being then reducedto zinc vapour and the zinc vapour then being condensed to zinc metal,characterized in that the zinc-sulphide concentrate is first heated in aneutral atmosphere wherebf the arsenic is almost completely removed; theremaining sulphur is then almost completely removed by roasting; theoxide zinciferous material obtained together with finely dividedcarbonaceous material, is introduced into, and entrained by, a movingstream of an oxygen-containing gas at such temperature that reduction tozinc vapour takes place and all other non-volatile components assume amolten free-flowing form; these other components are separated; and thezinc vapour condensed to give metallic zinc.

This sulphide concentrate advantageously contains copper and the oxidiczinciferous material is preferably free from lead and tin. The reasonsfor this are described below.

Preferably all the other components melt to a slag but the methodaccording to the invention may still be used if some components are notmelted, provided they are trapped in the molten slag and do not causethis to lose its free-flowing character.

The term oxidic zinciferous compounds include zinc oxide in the freeform (ZnO) or combined with acidic oxides (e.g. ZnCO or Zn SiO Thefinely divided oxidic zinciferous material and the carbonaceous materialpreferably separately (but possibly together) and one or both preferablybeing preheated may be introduced into the gas stream by variousmethods.

In one possible mode of operation, the reaction is carried out in afurnace chamber and the zinciferous and/ or the carbonaceous materialare dropped in at the top of the furnace. Alternatively, where asuitable inlet duct is provided for the oxygen-containing gas thezinciferous and/or carbonaceous material may be injected into theentering stream of gas in the inlet duct. If more than one such duct,e.g. a subsidiary duct, is provided a small proportion of the gas may beled through this to entrain the zinciferous and/ or carbonaceousmaterial. Also, at least the carbonaceous material may be introducedinto the moving stream of oxygen-containing gas in a separate entrainingstream of nitrogen. This is valuable when a carbonaceous fuel is usedpreheated to such an extent that there is danger of it igniting.

A pulverulent fiux, such as lime and silica, may be introduced into thestream of oxygen-containing gas when necessary in order to ensure thatthe slag formed is of suitable composition to become molten andfree-running.

In a preferred embodiment, the reduction is carried out in a whirlingcurrent of gas in a cyclone separator containing air or oxygen-enrichedair. The use of oxygenenriched air further improves the fuel economy byreducing the amount of nitrogen that has to be heated during theprocess.

The main bulk of the oxygen-containing gas required for the process isintroduced horizontally, e.g. through tuyeres in a direction oblique toand preferably tangentially to the radius of the cyclone cross-sectionso that it imparts a whirling, swirling, downwardly spiraling, motionand preferably a rotating motion to the charge. Uniform whirling orrotating motion of the air within the cyclone is generally to bepreferred, but turbulence may have a useful effect in certain instances.

The-carbonaceous material in the charge is conveniently pulverized cokebreeze or anthracite dust, which materials are cheaper than high-grademetallurgical coke; although other carbonaceous materials may be used,they should preferably be of low hydrogen content, and bituminous coalwith a high content of volatiles is therefore less suitable. Anyhydrogen present in the fuel finally appears in the gases partly ashydrogen and partly as water vapour, and it has been found that,although by means of the lead-splash condenser, zinc vapour can becondensed without any important amount of oxidation even in the presenceof considerable amounts of carbon dioxide, the presence of Water vapourin large amounts causes some oxidation of zinc vapour. In view of this,water should preferably be excluded as much as possible.

Preferably, according to the present invention the oxygen-containing gasis preheated, in order to improve the fuel economy of the process.

The relative amounts of carbon in the charge and of oxygen in the air(or other oxygen-containing gas, e.g. oxygen-nitrogen mixture) aregoverned by the consideration that the reaction of the carbon with theoxygen in the air and with the oxygen combined as zinc oxide must besuch as to form a mixture of carbon monoxide and carbon dioxide;preferably the CO /CO ratio by volume should lie between 0.6 and 1.6.The relative amounts of zinc oxide and carbon in the charge aredetermined by the consideration that the heat of combustion of thecarbon to a mixture of carbon monoxide and carbon dioxide must besufficient to provide heat for decomposing zinc oxide into Zinc vapourand oxygen, melting the slag, providing sensible heat for the gaseousreaction products and for heat losses, etc.

The invention further consists in zinc extracted by the method describedabove.

The invention still further consists in apparatus for extracting zinc bythe method as described above, comprising a refractory-lined (e.g. bricklined) cyclone; a slag chamber beneath the cyclone to collect the moltenmaterial running down the cyclone walls; and a condenser for zinc vapourconnected to an otftake in the slag chamber.

The slag chamber may have an upper tapping hole to run off the moltenmaterial from time to time and a lower tapping hole to empty thechamber, and may furthermore be fitted with one or more tuyeres toreduce further any zinc oxide contained in the slag. The cyclone mayhave external cooling coils or alternatively be Water-jacketed or havewater-cooled sections in the walls to minimise corrosion difficulties.The cyclone is preferably a vertical shaft of circular horizontalcross-section, so designed that the molten slag formed of moltendroplets which are thrown onto the cyclone walls by means of thecentrifugal action of the whirling gas. They then coalesce into a moltenslag which runs down the walls and can be collected at a horizontalotftake near the bottom, whence the gas, now free from slag, is conveyedto, e.g. a leadsplash condenser, which may be of the type described inBritish patent specification No. 572,961. Thus, -a gas/ liquidseparation takes place within the cyclone itself and this allows acleaner separation of the product gas from the liquid or solid products.The spiral movement of the gas within the chamber allows a longerretention time for the reduction of the zinc oxide to take place in thefurnace.

The invention will be more fully understood with reference to thefollowing discussion of the chemical reactions taking place.

If the zinciferous material being treated is an oxidized zincconcentrate of fairly high-grade (containing about 60% zinc) and if theair blast used is preheated to about 600 C., the amount of carbon neededis about 0.8 times the weight of zinc. Sufiicient air is introduced toburn approximately three quarters of the carbon to carbon monoxide andone quarter to carbon dioxide, so that this combustion may formally bewritten:

Typically for each gram-atom of zinc reduced, about 4.5 moles of carbonare consumed, and the initial combustion 4 of this carbon can beregarded as proceeding somewhat as follows:

4.5C+2.7O =3.6CO+0.9CO

The zinc oxide is then reduced by carbon monoxide:

ZnO+CO=Zn(g) +CO Adding these two equations together gives:

4.5C+2.7O +ZnO=2.6CO+1.9CO +Zn(g) Some carbon monoxide is used also inreducing ferric oxide to the ferrous state and in other minor reactions,so that the final gas may contain, with 1.0 mole zinc vapour, 2.4 molesCO and 2.1 moles CO with (if the oxygen was introduced as air) 10.3moles of nitrogen. After the zinc has been removed, the gas containsabout 14% CO and 16% CO. The combustion of this gas can be used toprovide the heat required for preheating the air introduced into thefurnace.

In order to ensure efficient condensation of zinc vapour to zinc metalin the lead-splash condenser, it is important that, apart from permanentgases, the gases conveyed to the condenser should contain no largeconcentrations of species other than zinc vapour, and in particularshould contain no vapours that can react with zinc vapour.

Amongst the elements that are volatilized under the conditions ofoperation are arsenic, sulphur, lead and tin. Arsenic is mainlyvolatilized as the element since under the condition of operation of thefurnace almost all arsenic compounds are decomposed with production ofarsenic vapour which interferes with condensation effi ciency byreacting with zinc to form zinc arsenide:

In the absence of lead or tin, sulphur is volatilized to only a limitedextent, probably as carbonyl sulphide (COS). In the presence of lead ortin, sulphur is volatilized to a much greater extent, and the sulphidesof these metals then react with zinc in the condenser to form zincsulphide:

In order to ensure good condensation efiiciency, it is necessary thatthe zinciferous material charged to the furnace should be substantiallyfree from arsenic, and either substantially free from sulphur orsubstantially free from lead and tin.

The commonest raw material for zinc production is a zinc sulphideconcentrate, which usually contains arsenic and lead as impurities. Wehave discovered that when such a zinc concentrate is heated in an inertatmosphere to a temperature within the range 950 C. to 1150 C. thearsenic is almost completely removed, and that this same treatmentremoves most of any lead, tin and cadmium contained in the concentrate.As an illustration of the possibility of volatilizing impurity metals(Pb, Cd and As) the following are the results of some experimental workin which samples of zinc blende were heated in a mufile furnace in whicha neutral or slightly reducing atmosphere was maintained:

Arsenic content of impure blend=0.l%

After /2 hour it had dropped to 0.0075

After 1 hour it had dropped to 0.0045

The zinc sulphide concentrate, with these impurities removed, can thenbe roasted to yield an oxidized product suitable for charging to thefurnace. This oxidised product contains only a small amount of sulphur,which, in the absence of lead and tin, is not volatilized to a greatextent when treated in the furnace according to the invention. Thepresence of copper in the charge is advantageous, since it combinesstrongly with the sulphur and hinders volatilization of sulphurcompounds.

The invention will be further described with reference to theaccompanying drawings, in which,

FIGURE 1 represents a vertical section along II of FIGURE 2 a cyclonefurnace for carrying out the method of the invention,

FIGURE 2 is a section along II-II of FIGURE 1,

FIGURE 3 is a section along III-III of FIGURE 1.

A cyclone 1 has an upper air inlet 2 with inlet orifice 2a and a loweroutlet throat 3, and is surrounded by cooling coils 4. The throat 3leads to a slag-collecting and zinc vapour receiving chamber 5 providedwith tapping holes 6 and 7 and tuyeres 8 and 9 to reduce any zinc oxidepresent in the slag. This slag-collecting chamber 5 has an offtake 10leading via duct 11 to a condenser system, for instance, a lead-splashcondenser (not shown).

It has been found convenient to make the cyclone furnace from thefollowing materials in the parts specified.

Lining of slag-collecting chamber 5: tapering portion ofcyclone-refractory concrete.

Cyclone and offtake covers: chrome-magnesite.

Exterior of slag-collecting chamber: insulating concrete.

Exterior of oiftake and of upper part of slag-collecting chamber:heat-insulating brick.

Lining of air-inlet 2 and upper part of cyclone: carborundum.

The cyclone furnace operates as follows:

Air (or oxygen-enriched air), roasted zinc concentrate and pulverisedfuel are blown in through inlet 2 and orifice 2a. The zinc oxide isreduced to zinc vapour and the solid constituents melt to a slag whichruns down the cooled cyclone walls into the slag chamber 5. The zincvapour is drawn off through the throat 3 up through olitake 10 and intoa condensing system, e.g. a lead-splash condenser.

The slag may be drawn off periodically through tapping hole 6, or whenit is desired to empty the chamber completely through tapping hole 7.The tuyeres 8 and 9 are provided for use if it is necessary to furtherreduce any zinc oxide retained in the slag, e.g. by use of morecarbonaceous fuel.

I claim:

1. In the method of smelting a mixed charge of finely divided oxidiczinciferous material and carbonaceous fuelreducing agent suspended in astream of oxygen containing gas moving downwardly in a verticallydisposed reduction zone, the improvement in combination therewith whichcomprises:

(a) the finely divided oxidic zinciferous material and the finelydivided carbonaceous fuel-reducing agent suspended in the stream ofoxygen containing gas are injected under pressure horizontally andtangentially into the upper portion of a vertically disposed reductionzone generally in the shape of a cyclone, with its larger end at the topand its smaller but open end at the bottom;

(b) a swirling downwardly spiraling motion of suflicient strength isimparted to the charge to cause it to pass into and around theperipheral upper portion of the cyclone-shaped reduction zone and intoand around the inwardly inclined peripheral lower portion of thecyclone-shaped reduction zone;

(c) the temperature of the upper and lower portions of the reductionzone is kept sufficiently high to oxidize the carbon in the charge to amixture of carbon dioxide gas and carbon monoxide reducing gas to reducethe zinc oxide in the charge with the carbon monoxide and to vaporizethe resulting zinc, and to melt non-volatilizable metal compoundsnormally present in the charge and carbon ash impurities to :a slag;

(d) the swirling downwardly spiraling motion of the charge is maintainedthroughout the reduction zone sufiiciently long to provide the detentiontime required to effect the reduction of the oxidic zinciferous materialand to melt the non-volatilizable metal compounds and ash impurities toa slag;

(e) the resultant droplets of molten slag are forced centrifugally tothe periphery of the inwardly inclined and gradually constricted lowerportion of the cyclone-shaped reduction zone;

(f) the droplets of molten slag are there coalesced and dropped throughthe open bottom of the cycloneshaped reduction zone, and gathered in amolten slag collecting zone, immediately below the reduction zone, as apool of molten slag;

(g) molten slag is tapped from the pool of molten slag;

and

(h) the resultant zinc vapour is passed downwardly from the reductionzone into the molten slag collecting zone and from above the top of thepool into a condensing system for the separate recovery of the 2. Methodaccording to claim 1, in which the reduction zone is externally cooledto increase the rate of heat loss from within the reduction zone.

3. Method according to claim 1, in which the oxidic zinciferous materialintroduced into the reduction zone is substantially free of lead, tin,cadmium, arsenic and sulphur.

4. Method according to claim 1, in which the zinciferous material isessentially in the form of zinc-sulphide concentrate; the concentrate isroasted to produce oxidic zinciferous material; and the resultant oxidiczinciferous material is introduced into the reduction zone.

5. Method according to claim 1, in which the zinciferous material isessentially in the form of zinc-sulphide concentrate containingcompounds of arsenic, lead, cadmium and sulphur as impurities; the zincsulphide concentrate is heated in an atmosphere inert to the metalcompounds normally present as impurities in the concentrate to decomposethe metal compounds and to volatilize and remove substantially all ofthe arsenic, lead and cadmium; the resulting arsenic-lead-cadmium freeconcentrate is roasted in the presence of air to remove nearly all ofthe remaining sulphur to produce a caleine consisting mainly of oxidiczinc; and the resultant oxidic zinciferous material is introduced intothe reduction zone.

6. Method according to claim 5, in which the zinciferous material in theform of zinc-sulphide concentrate containing copper is roasted in thepresence of the air to remove most of the sulphur and to form the oxidiczinciferous material of the charge; and the copper present in the chargeis combined with the remaining sulphur to hinder volatilization ofsulphur compounds in the reduction zone.

7. Method according to claim 1, in which a pulverulent flux is added toand is suspended in the suspended charge to help make the droplets ofslag molten and free-running and thus aid in their coalescence.

8. Method according to claim 1, in which a pulverulent flux in the formof an oxide is added to and is suspended in the suspended charge to helpmake the droplets of slag molten and free-flowing and thus aid in theircoalescence.

9. Method according to claim 1, in which a pulverulent flux selectedfrom the group consisting of lime and silica is added to and suspendedin the suspended charge to help make the droplets of slag molten andfree-flowing and thus aid in their-coalescence.

10. Method according to claim 1, in which a reducing agent is introducedinto the pool of molten slag to reduce zinc oxide present in the slag.

11. In apparatus for smelting a mixed charge of finely divided oxidiczinciferous material and carbonaceous fuelreducing agent suspended in astream of oxygen-containing gas moving downwardly in a verticallydisposed reduction shaft, the improvement in combination therewith whichcomprises:

(a) the vertically disposed reduction shaft of the smelting furnace isrefractory-lined and is in the shape generally of a cyclone with itslarger end at the top and its smaller end at the bottom, the lowerportion of the shaft being frusto-conical in shape, tapering 10downwardly and inwardly towards its lower end so that itscross-sectional area is gradually constricted to a bottom outlet throat;

(b) an insulated charge-feeding device connects the upper exteriorportion of the smelting furnace with the upper interior portion of thereduction shaft, the charge-feeding device having a conduit extendingtherethrough that connects the upper exterior portion of the smeltingfurnace with the upper interior portion of the reduction shafthorizontally and tangentially to permit the charge to assume a swirling,downwardly spiraling, motion,

(c) a combined slag collecting and Zinc vapour receiving chamber islocated immediately below the bottom of the vertical shaft to collect apool of molten slag and to permit separation of zinc vapour therefrom;

(d) at least one slag-tapping conduit extends through the Wall of theslag collecting chamber for removing molten slag therefrom; and

(e) a zinc vapour outlet offtake, separate and distinct from thereduction shaft, connects the upper portion of the slag collecting andzinc vapour receiving chamber for the passage of zinc vapour therefrom.

12. Apparatus according to claim 11, in which the smelting furnace isprovided with means for cooling the vertical reduction shaft to increasethe rate of heat loss from its reduction zone.

13. Apparatus according to claim 11,.in which the zinc vapour oiftakeconnects the upper portion of the slag collecting chamber with acondensing system for recovering zinc.

14. Apparatus according to claim 11,in which the slag References Citedby the Examiner UNITED STATES PATENTS 1,150,841 8/1915 Doherty 75-861,236,395 8/1917 Berglund 7586 1,923,511 8/1933 Scheil 756 1,977,11710/1934 Debuch 757 2,342,368 2/1944 Queneau 7586 XR 2,475,607 7/ 1949Garbo 7586 XR 2,530,078 11/ 1950 Ramsing 266-- XR 2,650,159 8/1953 Tarr6 2,951,756 9/1960 Cavanagh 7540 2,973,260 2/ 1961 Nogiwa 266-243,017,261 1/ 1962 Lumsden 75-86 FOREIGN PATENTS 921,861 5/ 1947 France.

30 HYLAND BIZOT, Primary Examiner.

BENJAMIN HENKIN, DAVID L. RECK, Examiners.

H. W. CUMMINGS, H. W. TARRING,

Assistant Examiners.

1. IN THE METHOD OF SMELTING A MIXED CHARGE OF FINELY DLIVIDED OXIDICZINCIFEROUS MATERIAL AND CARBONACEOUS FUELREDUCING AGENT SUSPENDED IN ASTREAM OF OXYGEN CONTAINING GAS MOVING DOWNWARDLY IN A VERTICALLYDISPOSED REDUCING ZONE, THE IMPROVEMENT IN COMBINATION THERWITH WHICHCOMPRISES: (A) THE FINELY DIVIDED OXIDIC ZINCIFEROUS MATERIAL AND THEFINELY DIVIDED CARRBONACEOUS FUEL-REDUCING AGENT SUSPENDED IN THE STREAMOF OXYGEN CONTAINING GAS ARE INJECCCTED UNDER PRESSURE HORIZONTALLY ANDTANGENTIALLY INTO THE UPPER PORTION OF A VERTICALLY DISPOSED REDUCTIONZONE GENERALLY IN THE SHAPE OF A CYCLONE, WITH ITS LARGER END AT THE TOPAND ITS SMALLER BUT OPEN END AT THE BOTTOM; (B)Z A SWIRLING DOWNWARDLYSPIRALING MOTION OF SUFFICIENT STRENGTH IS IMPARTED TO THE CHARGE TOCAUSE IT TO PASS INTO AND AROUND THE PERIPHERAL UPPER PORTION OF THECYCLONE-SHAPED REDUCTION ZONE AND INTO AND AROUND THE INWARDLY INCLINEDPERIPHERAL LOWER PORTION OF THE YCLONE-SHAPED REDUCTION ZONE; (C) THETEMPERATURE OF THE UPPER AND LOWER PORTIONS OF THE REDUCTION ZONE ISKEPT SUFFICIENTLY HIGH TO OXIDIZE THE CARBON IN THE CHARGE TO A MIXTUREOF CARBON DIOXIDE GAS AND CARBON MONOXIDE REDUCING GAS TO REDUCE THEZINC OXIDE IN THE CHARGE WITH THE CARBON MONOXIDE AND TO VAPORIZED THERESULTING ZINC, AND TO MELT NON-VOLATILIZABLE METAL COMPOUNDS NORMALLYPRESENT IN THE CHARGE AND CARBON ASH IMPURITIES TO A SLAG; (D) THESWIRLING DOWNWARDLY SPIRALING MOTION OF THE CHARGE IS MAINTAINEDTHROUGHOUT THE REDUCTION ZONE SUFFICIENTLY LONG TO PROVIDE TO DETENTIONTIME REQIRED TO EFFECT THE REDUCTION OF THE OXIDIC ZINCIFEROUS MATERIALAND TO MELT THE NON-VOLATILIZABLE METAL COMPOUNDS AND ASH IMPURITIES TOA SLAG; (E) THE RESULTANT DROPLETS OF MOLTEN SLAG ARE FORCEDCENTRIFUGALLY TO THE PERIPHERY OF THE INWARDLY INCLINED AND GRADUALLYCONSTRICTED LOWER PORTION OF THE CYCLONE-SHAPED REDUCTION ZONE; 8F) THEDROPLETS OF MOLTEN SLAG ARE THERE COALESCD AND DROPPED THROUGH THE OPENBOTTOM OF THE CYCLONESHAPED REDUCTION ZONE, AND GATHERED IN A MOLTENSLAG COLLECTING ZONE, IMMEDIATELY BELOW THE REDUCTION ZONE, AS A POOL OFMOLTEN SLAG; (G) MOLTEN SLAG IS TAPPED FROM THE POOL OF MOLTEN SLAG; AND(H) THE RESULTANT ZINC VAPOUR IS PASSED DOWNWARDLY FROM THE REDUCTIONZONE INTO THE MOLTEN SLAG COLLECTING ZONE AND FROM ABOVE THE TOP OF THEPOOL INTO A CONDENSING SYSTEM FOR THE SEPARATE RECOVERY OF THE ZINC. 11.IN APPARATUS FOR SMELTING A MIXED CHARGE OF FINELY DIVIDED OXIDICZINCIFEROUS MATERIAL AND CARBONACEOUS FUELREDUCING AGENT SUSPENDED IN ASTREAM OF OXYGEN-CONTAIN ING GAS MOVING DOWNWARDLY IN A VERTICALLYDISPOSED REDUCTION SHAFT, THE IMPROVEMENT IN COMBINATION THEREWITH WHICHCOMPRISES: (A) THE VERTICALLY DISPOSED REDUCTION SHAFT OF THE SMELTINGFURNACE IS REFRACTORY-LINED AND IS IN THE SHAPE GENERALLY OF A CYCLONEWITH ITS LARGER END AT THE TOP AND ITS SMALLER END AT THE BOTTOM,THELOWER PORTION OF THE SHAFT BEING FRUSTO-CONICAL IN SHAPE, TAPEROINGDOWNWARDLY AND INWARDLY TOWARDS ITS LOWER END SO THAT ITSCROSS-SECTIONAL AREA IS GRADUALLY CONSTRICTED TO A BOTTOM OUTLET THROAT;(B) AN INSULATED CHARGE-FEEDING DEVICE CONNECTS THE UPPER EXTERIORPORTION OF THE SMELTING FURNACE WITH THE UPPER INTERIOR PORTION OF THEREDUCTION SHAFT, THE CHARGE-FEEDING DEVICE HAVING A CONDUIT EXTENDINGTHERETHROUGH THAT CONNCTS THE UPPER EXTERIOR POROF THE SMELTING FURNACEWITH THE UPPER INTERIOR PORTION OF THE REDUCTION SHAFT HORIZONTALLY ANDTANGENTIALLY TO PERMIT THE CHARGE TO ASSUME A SWIRLING, DOWNWARDLYSPIRALING, MOTION, (C) A COMBINED SLAG COLLECTING AND ZINC VAPOURRECEIVING CHAMBER IS LOCATED IMMEDIATELY BELOW THE BOTTOM OF THEVERTICAL SHAFT TO COLLECT A POOL OF MOLTEN SLAG AND TO PERMIT SEPARATIONOF ZINC VAOUR THEREFROM; (D) AT LEAST ONE SLAG-TAPPING CONDUIT EXTENDSTHROUGH THE WALL OF THE SLAG COLLECTING CHAMBER FOR REMOVING MOLTEN SLAGTHEREFROM; AND (E) A ZINC VAPOUR OUTLET OFFTAKE, SEPARATE AND DISTINCTFROM THE REDUCTION SHAFT, CONNECTS THE UPPER PORTION OF THE SLAGCOLLECTING AND ZINC VAPOUR RECEIVING CHAMBER FOR THE PASSAGE OF ZINCVAPOUR THEREFROM.